Magnetic resonance evaluation of ventrolateral medullary compression in essential hypertension

Object. The authors designed a blinded prospective study comparing patients with essential hypertension to patients without hypertension in which magnetic resonance (MR) imaging was used to evaluate the role of lateral medullary compression by adjacent vascular structures as a cause of neurogenic hypertension. Methods. Patients with documented essential hypertension were recruited to undergo thin-slice axial brainstem MR imaging evaluation. Nonhypertensive (control) patients scheduled to undergo MR imaging for other reasons also underwent thin-slice MR imaging to form a basis for comparison. Magnetic resonance images obtained in patients from the hypertensive (30 patients) and the control (45 patients) groups were then compared by four independent reviewers (two neuroradiologists and two neurosurgeons) who were blinded to the patients' diagnosis and hypertensive status. Images were reviewed with regard to left versus right vertebral artery (VA) dominance, compression of the medulla on the left and/or right side, and brainstem rotation. Medullary compression was graded as either vessel contact without associated brainstem deformity or vessel contact with associated brainstem deformity. Conclusions. There was a tendency toward left VA dominance in the hypertensive group compared with the control group, although a significant difference was shown by only one of the four reviewers. There were no differences in brainstem compression or rotation between the hypertensive and nonhypertensive groups. These results are contrary to those of recently published studies in which MR imaging and/or MR angiography revealed lateral brainstem vascular compression in hypertensive patients but not in nonhypertensive (control) patients. Reasons for this discrepancy are discussed. On the basis of their own experience and that of others, the authors believe that neurogenic hypertension does exist. However, thin-slice MR imaging may not be a reliable method for detecting neurovascularly induced essential hypertension and the prevalence of neurovascular compression as the source of hypertension may be overestimated when using current imaging techniques.